Flat conductor cable (FCC) underlying carpet tiles is in present use to supply electrical power to various points of use, as for example, handling lighting and appliance loads in commercial buildings. The flat conductor cable includes in a common form thereof a plurality of flat conductors i.e., live, neutral and ground conductors encased in a plastic electrically insulative casing and additionally having a metallic shield disposed at the upper surface of the cable. A layer typically made of tough insulation material may be provided on the bottom of the cable as an abrasion protection shield. The metallic shield is electrically grounded to provide against electrical hazard, such as accidental piercing of the shield and the live conductor by an object, which object, since the shield is connected to ground, is rendered unhazardous to a person who might contact same. An advantage of the use of this type of conductor cable is the ease with which it can be installed beneath carpeting while at the same time allowing for transfer of power therefrom at selected locations, pedestals or transfer receptacles being installed for such purpose.
Various specialized types of devices including receptacles are known for establishing power take-off from the flat conductor cable at a given location as well as for effecting splicing of a branch line to a main. Thus, for connecting a receptacle at a desired location, a terminal block carrying insulation-piercing members or contacts can be secured over the flat conductor cable with the contacts piercing the flat conductor cable to establish continuity with the respective cable conductors. A receptacle can then be placed over the terminal block with suitable connection between the terminals of the block and contact points in the receptacle being made with round wire discrete conductors. With such installation the cable run can be terminated at the take-off location or it may pass through the terminal block so that additional receptacles can be connected further down the line.
It is also known to use, for purposes of providing power take-off, a direct contact receptacle which embodies insulation-displacement contacts (IDC's) therein and employed when installed directly over a conductor cable to have these piercing contacts electrically connectively engage the conductors in the cable. Such a receptacle is shown in commonly-assigned U.S. Pat. No. 4,479,692 issued on Oct. 30, 1984 and entitled "Receptacle for Flat Multi-Conductor Cable".
The increased use of desktop computers and other microprocessor based products which handle digital input signals has led to specialized power requirements to protect against line "noise" or interference. In general, attempts at meeting these requirements are being made through the use of power line filters or conditioners. Additionally, a power line grounding conductor to the receptacle grounding terminal for that equipment is being run separate from the ground conductor which connects the receptacle mounting frame to the grounding point of the building. Such ground provisions are referred to as "isolated ground" circuits and require that in addition to a neutral and live conductor, there be two other conductors, one each for separate ground paths. One path is exclusively used for sensitive equipment, such as desktop computers.
In buildings wired with round conductors, the installation of an isolated ground receptacle presents little difficulties. The junction boxes and floor pedestals can readily accommodate the extra conductor and provide for its proper connection. However, in buildings wired with flat conductor cable installed under carpets, the installation of an isolated ground receptacle creates more of a problem. Various techniques are known by which a receptacle can be connected to four or five conductor flat conductor cable. Until recently, these techniques involved making a transition from the flat cable to round jumper wire and then making the connections to those round jumper wires. A recent development as described in commonly-assigned U.S. patent application Ser. No. 630,794 filed on July 13, 1984, by the inventors herein and entitled "Device for Flat Multiconductor Cable Connection", discloses a device which provides for a direct contact receptacle to be connected to a selected live conductor in the four or five conductor cable. This device does not provide a means by which the receptacle grounding terminal may be connected to a conductor other than that connected to the building ground. Accordingly, it is desirable to provide a means for installing a direct contact receptacle to an isolated ground circuit without need of additional round jumper wires.